[mowbot] Buried Boundary

KEN_REED nospam at HP-Boise-om2.om.hp.com
Tue, 29 Jul 97 09:40:04 -0600

Dave,

Just read your post on the Mowbot mailing list. I've always found
your insight into problems a pleasure, and have enjoyed seeing your
designs. Don't be critical of yourself, you have solved a lot of
problems for yourself and helped others along the way. Most of this
you will reuse.

Some random thoughts with respect to boundary marking using an
electromagnetic signal.

Have you looked at the "radio" fences for pets? They seem to
have detection up to about 0.6 meters above the cable. One may
be able to use one of these almost intact, or reverse engineer
one.

Does Tandy carry a "buried treasure finder", if they do, one
nice thing about Tandy is that you can get the service manuals
and schematics for just about all the items they sell. Be
persistent, they are available no matter what the clerk at the
local store may tell you. I've bought several service manuals
for things I never owned, just to see how they did it.

Have you looked in any of the "Encyclopedia of Electronic
Circuits" type books. There will probably be several designs in
there. Is there an EEC on the web?

I liked your idea of using the buried cable for more than
boundary marking. You could bury several different coded cables,
1) absolute boundary, 2) path to charger, 3) path to back yard
over the driveway, 4) mow on even days, 5) mow on odd days, etc.,
you get the idea. They could be differentiated by frequency, or
waveform.

For testing various frequencies, waveforms, transformers, or
drivers you may want to use a coil of wire attached to a scope
probe as the detector. Which is the best transmission
arrangement, open loop wire, closed loop circuit, di-pole
arrangement? After you determine the optimum transmission
parameters for the earth/grass/air path, then start working on
detectors. Be sure to test with wet and dry ground since that
could affect the path's impedance by orders of magnitude.

bye for now and good luck


ken reed
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